Dates do not get passed to formatter

[jeffijoe]

const logger = new Bristol()
logger.addTarget(function() {}).withFormatter(function() {
  console.log(arguments[3])
})
logger.error('hey ho', { here: 'we go' }, 123, new Date())

This is what I see in the console:

    [ 'hey ho',
      123,
      { file: '/Users/jeff/Projects/bristol-stackdriver/src/__tests__/index.test.ts',
        line: '20',
        here: 'we go' } ]

Am I missing something? 😄